The present invention relates to a device to control the trailing axle of a vehicle. More particularly, the present invention relates to a device to control the height of a rear end portion of a vehicle having at least two rear axles, where one rear axle serves as a driving axle and another rear axle serves as a trailing axle. Such a device is known from DE-OS 34 16 422.
This known device for controlling the height of a vehicle with a trailing and a driving axle typically has air suspension bellows and valves. A first valve arrangement can selectively connect the air suspension bellows of the driving axle to a pressure fluid source or sink. Alternatively, the first valve arrangement can isolate the air suspension bellows of the driving axle.
Similarly, a second valve arrangement can selectively connect the air suspension bellows of the trailing axle to the air suspension bellows of the driving axle or to the pressure fluid sink. Alternatively, the second valve arrangement can isolate the trailing axle bellows thus interrupting its connection with the driving axle bellows. The operation and function of this known device are discussed below.
In normal operation, the second valve arrangement connects the air suspension bellows of the driving axle to the air suspension bellows of the trailing axle. This allows the same pressure to prevail in the air suspension bellows of both the driving and the trailing axles.
As used herein, an input receives a connection from a previous circuit, an output provides a connection to the next circuit, and an outlet connects the particular circuit to a pressure fluid sink vented to the atmosphere.
The first valve arrangement, which consists of a first valve and a second valve, is then switched over. This interrupts the connection between the pressure fluid supply container and the second valve. (The output of the first valve is disconnected from its input). The switched first valve arrangement also connects the pressure fluid line, going from the first valve to the second valve, to the atmosphere via the first valve. (The output of the first valve is connected to its outlet). Furthermore, the second valve disconnects the pressure fluid line, going from the second valve to the air suspension bellows, from the vented pressure fluid line. (The output of the second valve is disconnected from its input).
The vehicle structure is raised by increasing the air volume in the air suspension bellows. The valves of the first and second valve arrangements are actuated electrically to connect the air suspension bellows to the pressure supply container. When a desired vehicle height (distance between the vehicle axles and the vehicle structure) is reached, the valves are switched over to isolate the air suspension bellows from the pressure supply container and the pressure fluid sink (i.e., the atmosphere).
Conversely, the vehicle structure is lowered by decreasing the air volume in the air suspension bellows. The valves of the first and second valve arrangements are actuated electrically to connect the air suspension bellows to the pressure fluid sink. When a desired vehicle height is reached, the second valve of the first valve arrangement is switched over to isolate the air suspension bellows.
To put a heavy load on the driving axle of the vehicle under unfavorable road conditions, such as slippery or loose road surfaces, the pressure in the air suspension bellows of the trailing axle is decreased. This is accomplished by switching over the second valve arrangement consisting of two valves. The switching disconnects the air suspension bellows of the trailing axle from the air suspension bellows of the driving axle. Furthermore, the switching connects the air suspension bellows of the trailing axle to the pressure fluid sink.
If it is desired to maintain the pressure in the air suspension bellows of the trailing axle and at the same time disconnect it from the air suspension bellows of the driving axle, then both valves of the second valve arrangement are actuated.
To be able to carry out the above-described functions, it is necessary to provide each of the four valves with a solenoid for the actuation of the valves. Furthermore, it is necessary to provide several electric lines which require a plurality of pins on a plug to connect the electric lines to a control device.
It is the object of the instant invention to decrease the number of required solenoid activated valves of the above mentioned device while maintaining all the mentioned functions of the known device.
In particular, this invention offers the advantage that it is possible to change the air volume in the pressure fluid chambers of the driving and trailing axles of a vehicle at minimal cost. Furthermore, the air volume in the pressure fluid chambers of the trailing axle is maintained independently of the air volume in the pressure fluid chambers of the driving axle.